Thermally insulated and counterweighted roof



y 3, 1966 M. NACHSHEN 3,249,251

THERMALLY INSULATED AND COUNTERWEIGHTED ROOF Filed Dec. 26, 1963 3 Sheets-Sheet 1 INVENTOR Maurice Nochshen ATTORNEY May 3, 1966 M. NACHSHEN 3,249,251

THERMALLY INSULATED AND COUNTERWEIGHTED ROOF Filed Dec. 26, 1965 3 Sheets-Sheet 2 INVENTOR Maurice Nochshen BY yw OZZ/M ATTORNEY FIG. 5

y 3, 1966 M. NACHSHEN 3,249,251

THERMALLY INSULATED AND COUNTERWEIGHTED ROOF Filed Dec. 26, 1963 3 Sheets-Sheet 3 INVENTOR M aurice Nachshen ATTORNEY or more directions.

United States Patent This invention relates to a roof suitable for a ground reservoir.

Ground reservoirs are particularly suitable for storing a liquefied gas, that is a liquid which boils at atmospheric pressure at a temperature below the ambient temperature. Examples of liquefied gases are liquefied nitrogen,

' liquefied air, liquefied methane, liquefied natural gas, liquefied oxygen and liquefied propane.

In the past when storing many liquefied gases in ground reservoirs the roofs have had to be anchored round the periphery of the reservoir because of the pressure of the gas due to the boil-off. This has usually entailed a large mass of concrete at the periphery and long anchor bolts. Also for large reservoirs it has usually been necessary to make the roof and superstructure of costly metal which does not become brittle at the low temperatures of the liquefied gas.

Such disadvantages are at least obviated by the use of a roof according to this invention which comprises a flat or cambered sheet lined on at .least one surface with thermal insulation, a superstructure to which the sheet is attached, and a counterweight acting on said sheet.

Furthermore according to the invention a ground reservoir suitable for storing a liquefied gas is one in which there is a hole in the surface of the ground, which hole is impervious to the substance to be stored, a gas vent, conduit and pumping means for filling and emptying the reservoir, and a roof comprising a flat or cambered sheet lined on at least one of the surfaces with thermal insulation, a superstructure to which the sheet is attached, and a counterweight acting on said sheet.

A preferred hole in the surface of the ground is one wherein the ground formation surrounding the hole contains a liquid which will solidify when the reservoir is charged with the substance to be stored. An example of such a structure is shown in the US. application of Proctor et al., Serial No. 283,019, filed May 24, 1963.

The sheet which is attached to the superstructure is' preferably of thin metal e.g. a metal membrane. The most suitable metals are those which do not become embrittled at low temperatures e.g. high nickel steels, stainless steels, copper, aluminium or aluminium alloys. Usually the metal membrane is stiffened by small ribs in two Instead of a metal sheet, sheets of other materials e.g. plywood, could be used.

The sheet is preferably substantially flat, but may if desired be cambered. In order to protect the sheet from the cold, when the roof is used for a ground reservoir for liquefied gases, the sheet should preferably be lined with insulation on the underside, although insulation may be used on the top side if desired.

The thermal insulation may be of fibre glass, foamed plastic (e.g. polyurethane foam or polystyrene foam), balsa Wood, paper honeycomb, kapok, mineral wool or rock wool. It is necessary to support the thermal insulation lining which is on the underside of sheet. A very suitable insulation support isa wire mesh or expanded metal grid, but other suitable insulation supports include rigid sheets of plywood, wall board, fibre board, woodwool or similar materials preferably suspended from the 3,249,251 Ice Patented May 3, 1966 roof sheet at the points where the latter is supported from the superstructure.

The superstructure may comprise steel ribs. Such ribs may be spaced at intervals across the roof and should preferably intersect each other (e.g. at right angles), to form a grid. In the case of a circular roof they may all meet one another at the centre thereby acting as radial ribs. The ribs are preferably curved, so that together they form a dome shaped superstructure.

Other suitable forms of superstructure are girders or trusses of any suitable material (e.g. metal or wood) and arranged in spaced parallel rows, or intersecting each other, or arranged radially.

It is of course essential that part of the superstructure should extend beyond the sheet so that the roof can be supported or fixed in position.

The sheet is preferably attached by means of hangers flexible in the horizontal direction (to allow for thermal contraction) and fixed to the superstructure and the sheet. These hangers should preferably be regularly spaced so as to give an evenly spaced support to the sheet. When the superstructure is in the form of a grid, these hangers may be fixed to the superstructure at the intersections of the grid members. The attachment of the hangers to the sheet should preferably be at the stifieners.

The means by which the sheet is attached to the superstructure should have a cold break 'to prevent heat being conducted from the superstructure to the sheet. A suitable cold break is thermal insulation breaking the direct connection between the sheet and superstructure. When hangers are used each one is preferably provided with a block of thermal insulation situated between the two ends of the hanger. Another way in which a cold break is provided is for each other hanger to comprise two linked elements, each element being lined with thermal insulation.

The counterweight should preferably be arranged so as to give a regularly distributed downward thrust to the sheet. The counterweight can be of blocks of material sufficient in weight to offset any upwards thrust on the sheet and insulation e.g. due to boil-oil of a liquefied gas. Preferably the magnitude of the counterweight is not much more than is necessary, otherwise there is unnecessary strain on the component parts of the roof. Suitable counterweights are weight controlled blocks of metal or wood, or concrete (either dense of light weight), sand or gravel. The counterweight material may also serve as additional insulation.

If the sheet is likely to be at the freezing point of water or at a lower temperature, there should preferably be a vapour barrier placed above the counterweightmaterial and arranged in sealing relationship with any hangers of sheet supports. Suitable vapour barriers are plastic sheets e.g. polyethylene sheets, although bitumen fabric sheets could be used.

The roof may be fitted with liquid inlet, liquid and vapour outlets, and safety outlet valves if desired. In addition, especially when the roof is used for ground reservoirs for storing liquefied gas such as liquid methane, the roof may be provided with a gas seal. A suitable gas seal is described in the specification of co-pending U.S. application Serial No. 154,520 of Schlum-berger et al., filed November 24, 1961. When the sheet of the roof of the present invention is a metal membrane it may be conveniently extended at its perimeter and inserted in a slot in the earth as described in the above specification.

A preferred form of roof according to the invention is now described with reference to the accompanying drawings.

In FIGURE 1 a cross-sectional elevation of the roof covering a ground reservoir is shown.

tune by hangers 21 having cold breaks 15.

In FIGURE'Z a plan view of the roof of FIGURE 1 on a reduced scale is shown.

In FIGURE 3 a perspective view of the roof of FIG- URE 1 with part cut away is shown.

In FIGURE 4 a roof with a different form of super-- structure is shown.

In FIGURE 5 a cross-sectional elevation of another form of roof covering a ground reservoir is shown.

. InFIGURE 6 a plan view of the roof of FIGURE 5 on a reduced scale is shown.

FIGURE 7 is a cross-sectional elevation of a detail showing one form of hanger and cold-break.

Referring to FIGURES 1 to 3, an aluminium membrane 1 is supported by steel hangers 5 attached to the intersections of curved steel ribs 6 and curved steel ribs 7."

Gas vent 23 and conduit 24 are indicated schematically and may be of any conventional design.

In FIGURE .4 the curved ribs 13 do not intersect but meet at a point thereby acting as radial trusses.

. ,Referring to FIGURES 5 and 6, the superstructure comprises trusses 14 which is supported on reinforced concrete or steel columns 19;. A cambered aluminium decking 16 lined with supported insulation 17 and loaded with counterweight 18 is suspended from the superstruc- A gas seal 20 seals the end of the sheet 16.

Asan alternative the trusses may intersect one another to form a grid structure similar to that shown in FIG- URE 2, or may meet one another at a point thereby acting as radial trusses to form a structure similar to that shown in FIGURE 4.

FIGURE 7 shows one manner in which the hangers 5 may support theroof structure. The cold-break 12 may be ,of any construction which provides a heat-insulating element in hangers 5 so as to impede the flow of heat. As shown, a block of thermal insulation 12a, which maybe cork, ceramic or any other suitable heat. insulatingmaterial, is interposed between sections 5 and 5' of the hanger so that the insulating material 12a is subject to compressive force only. Section 5 of the hanger may be of mild steel but section 5' should be .of cold resisting material such as stainless steel. The impervious roof sheet 1 is preferably provided with a plurality of 4 ribs 1a, extending in the direction shown, and at right angles to that direction.

Hangers 5': support the roof sheet 1 in any suitable manner, e.g. as shown in FIGURE 7 by means of a nut 5a under a washer 5b at intersections of the ribs 1a and lb. The ribs,-nut and washer should be of cold resisting material. The grid 3 may suitably be made of aluminium wire mesh or expanded aluminium sheet or other cold resisting material capable of supporting the insulation 2. The grid 3 may suitably be supported by ribs 3;: hung by means of hangers 3b 'of bent rod from the ribs 111 and 1b.

Above the roof sheet 1 is placed weighting material 4, which may be sand, gravel, concrete, etc., and is shown in the form of concrete blocks or bars, which should be more or less uniformly distributed over the sheet 1. A vapor barrier 4a is placed above theweighting material 4 to insulate the roof sheet 1 from atmospheric moisture.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and, arrangement within the scope of my invention, as defined in the appended claims.

I claim:

1. A ground reservoir for storing liquid at temperatures considerably below the freezing point. of water, said reservoir comprising a hole formed in the surface of the ground, a roof covering the top of said hole, said roof comprising an impervious thin lightweight membrane sheet, a mechanically rigid open framework superstructure, a plurality of hanger means under tension for supporting said sheet at .a plurality of points from said superstructure, and counterweightmeans distributed over and supported above said sheet and below said superstructure for [resisting upward gas pressure acting on the lower surface of said sheet; I

2. The invention according to claim 1, said hanger means being flexible in the horizontal direction to permit thermal contraction and-expansion of said sheet.

References Cited by the Examiner LOUIS G. MANCENE, Primary Examiner.

GEORGE E. LOWRANCE, THERON E. CONDON,

Examiners. 

1. A GROUND RESERVOIR FOR STORING LIQUID AT TEMPERATURES CONSIDERABLY BELOW THE FREEZING POINT OF WATER, SAID RESERVOIR COMPRISING A HOLE FORMED IN THE SURFACE OF THE GROUND, A ROOF COVERING THE TOP OF SAID HOLE, SAID ROOF COMPRISING AN IMPERVIOUS THIN LIGHTWEIGHT MEMBRANE SHEET, A MECHANICALLY RIGID OPEN FRAMEWORK SUPERSTRUCTURE, A PLURALITY OF HANGER MEANS UNDER TENSION FOR SUPPORTING SAID SHEET AT A PLURALITY OF POINTS FROM SAID SUPERSTRUCTURE, AND COUNTERWEIGHT MEANS DISTRIBUTED OVER AND SUPPORTED ABOVE SAID SHEET AND BELOW SAID SUPERSTRUCTURE FOR RESISTING UPWARD GAS PRESSURE ACTING ON THE LOWER SURFACE OF SAID SHEET. 